1. Field of the Invention
The present invention relates to image scanning apparatuses.
2. Description of the Related Art
When an image scanning apparatus is used in a low temperature environment such as a cold region or an early morning in winter, condensation sometimes occurs on a surface of an optical unit such as a mirror and results in a fall in reflectance, transmittance, or the like, and consequently, an image is scanned darkly and in a low quality. Therefore, an image scanning apparatus includes a heater to prevent from condensation, and performs heating with the heater to warm-up before an image scan.
For example, a known mechanism to prevent from condensation automatically performs heating at a predetermined time or performs heating when it is estimated that condensation occurs on the basis of temperature and humidity. The aforementioned mechanism may perform heating, although condensation does not actually occur. Consequently, it wastes electric power. To solve this problem, an image scanning apparatus estimates that condensation occurs and performs heating when a difference between the last shading data on yesterday and the initial shading data on today is equal to or larger than a predetermined threshold value.
However, in the case that it is estimated whether condensation occurs or not in the aforementioned manner, for example, if condensation occurred when the last shading data on yesterday was obtained, then condensation that currently occurs may not be detected.